Abstract [en]

Prolonged exposure to palmitate impairs beta-cell function and mass. One of the proposed mechanisms is alteration in ceramide generation. In the present study, exposure to palmitate induced the level of palmitoyl transferase and ceramide synthases, enzymes of the ceramide de novo and salvage pathways, and doubled total ceramide levels, which was associated with decreased insulin secretion and augmented apoptosis in MIN6 cells and human islets. By inhibiting enzymes of the pathways pharmacologically with ISP-1 or fumonisin B1 or by siRNA we showed that Cer(14:0), Cer(16:0), Cer(20:1) and Cer(24:0) species, generated by the salvage pathway, are linked to the harmful effect of palmitate on beta-cells. Oleate attenuates negative effects of palmitate on beta-cells. When oleate was included during culture of MIN6 cells with palmitate the palmitate-induced up-regulation of the enzymes of the de novo and salvage pathways was prevented resulting in normalized levels of all ceramide species except Cer(20:1). Our data suggest that enhanced ceramide generation in response to elevated palmitate levels involves both de novo and salvage pathways. However, the negative effects of palmitate on beta-cells are attributed to generation of ceramide species Cer(14:0), Cer(16:0) and Cer(24:0) via acylation of sphingosine.